title: Ultrasound-guided peripheral regional anaesthesia: a feasibility study in obese versus normal-weight women.
abstract: OBJECTIVE
  In particular, obese patients may profit from peripheral regional anaesthesia due to avoidance of general anaesthesia. Currently, ultrasound (US) guidance is described as the golden standard in regional anaesthesia, but no studies have so far evaluated the US behaviour of peripheral nerve structures in obese versus normal-weight patients. To be able to perform such studies, it is necessary to develop new and more objective methods to quantify nerve visibility by US. We therefore designed a prospective, observational, comparative and blinded study to investigate the visibility of peripheral nerves in obese versus normal-weight patients by using a novel method based on histogram grey-scale values.
  
  
  METHODS
  We scanned the median and sciatic nerves in 40 obese and normal-weight female patients and calculated differences of histogram grey-scale values between nerves and surrounding tissues.
  
  
  RESULTS
  Histogram value analysis showed less US visibility of sciatic nerves in obese versus normal-weight study patients, which is caused by higher surrounding tissue histogram values. No differences could be detected for median nerves.
  
  
  CONCLUSIONS
  The novel technique of comparing histogram grey-scale values to determine the visibility of the peripheral nerve in different patient categories was found feasible. Median nerves are appropriately visible by US in both normal and obese subjects, whereas sciatic nerves are less visible in obese as compared with normal-weight women. Our results serve as the rationale behind difficulties in peripheral regional anaesthesia in obese patients.
authors.affiliation: Department of Anaesthesia, Intensive Care Medicine and Pain Therapy, Medical University of Vienna, Vienna, Austria.
authors.forename: P
authors.initials: P
authors.lastname: Marhofer
authors.affiliation: Department of Anaesthesia, Intensive Care Medicine and Pain Therapy, Medical University of Vienna, Vienna, Austria.
authors.forename: B
authors.initials: B
authors.lastname: Pilz-Lubsczyk
authors.affiliation: Section of Anaesthesiology and Intensive Care, Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: P-A
authors.initials: PA
authors.lastname: Lönnqvist
authors.affiliation: Department of Anaesthesia, Intensive Care Medicine and Pain Therapy, Medical University of Vienna, Vienna, Austria.
authors.forename: E
authors.initials: E
authors.lastname: Fleischmann
mesh_terms: D000328:Adult; D000765:Anesthesia, Conduction; D000768:Anesthesia, General / Q000009:adverse effects / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009765:Obesity; D010525:Peripheral Nerves / Q000000981:diagnostic imaging*; D011446:Prospective Studies; D012016:Reference Values; D012867:Skin / Q000000981:diagnostic imaging*; D013851:Thinness; D018084:Ultrasonography, Interventional